An inter-switch link (ISL) is a frame-based communications link used to interconnect two or more networking switching devices. Referring to FIG. 1, local area networks (LANs) 101 and 110 can be interconnected using an inter-switch link (ISL) 120 between LAN switching and routing devices 105 and 115. The ISL interconnection 120 interconnects LANs 101 and 110 and allows the nodes 102-103 on the first LAN 101 to exchange data with the nodes 111-113 on the second LAN 110.
An ISL can transport a variety of native frame types between routing and interface devices. Token Ring, Ethernet and other native LAN data frames may be transferred between a pair of gateway switches interconnected by an ISL. To transport a native LAN data frame, the LAN data frame is encapsulated within an ISL frame and transported across the ISL as payload data within the ISL frame. ISL frame header data identifies the type of LAN data frame being transported and may indicate the destination of that frame. A network interface device terminating an ISL link may receive a mix of encapsulated frame types. For example, a network gateway may receive both Ethernet frames and Token Ring frames encapsulated within ISL frames.
Data frames may be exchanged between local area network switches and computer devices using an inter-switch link. An inter-switch link transfers frames of data that encapsulate native LAN data frames. Inter-switch link frame formats may differ depending on the type of native LAN data frame that is encapsulated. Inter-switch link frame processing efficiency at a receiving or transmitting device may be improved by maintaining consistent inter-switch link frame formats.
In general, in one aspect, the invention features a method of transmitting data between an interface device and an inter-switch link. The method includes receiving a frame on the inter-switch link and determining whether the frame""s payload is an encapsulated frame. The method also includes forming a modified frame when the first payload is an encapsulated frame. The modified frame header includes a subset of data from the received frame""s header.
In general, in another aspect, the invention features a method of transmitting data between a peripheral bus and an inter-switch link. The method is implemented in an interface device and includes receiving a frame over the peripheral bus, determining whether the frame""s payload is an encapsulated frame, and modifying the received frame if the payload is an encapsulated frame. Modified frames are then transmitted on the inter-switch link. Modified frames include a modified header having data from the received frame""s header and data from the received frame""s trailer.
Implementations may include one or more of the following features. The received and modified frames also may include trailer regions. The trailer of the modified frame may include data from the received frame""s header. Frame trailers may include error control data. Forming the modified frame may include calculating error control data. Encapsulated frames may be of more than one frame type. For example, encapsulated frames may be either Token Ring frames or Ethernet frames. Modified frames may be formed for a subset of frame types. The interface device also may transmit modified frames over a peripheral bus using a direct memory access bus transfer.
In general, in another aspect, the invention features a link interface device. The link interface device includes a data transmitting and receiving unit, frame type detection circuitry, and frame modification circuitry. The data transmitting and receiving unit couples the device to an inter-switch link to transmit and receive data frames on the link. The frame type detection circuitry can receive data frames from the transmitting and receiving unit and can determine whether a payload segment in the received data frame is an encapsulated frame. The frame modification circuitry is coupled to the frame type detection circuitry and can modify frame header segment data when the payload segment in the received frame is an encapsulated frame.
Implementations may include one or more of the following features. The device may include bus interface circuitry coupling the device to a peripheral bus over which data frames are transmitted and received. For example, the bus interface circuitry may implement a peripheral component interconnect (PCI) interface to couple the device to a PCI bus. Additionally, the bus interface circuitry may include direct memory access (DMA) circuitry configurable to initiate DMA data transfers to and from the device to a memory region accessible over the bus.
Implementations may provide one or more of the following advantages. Local area network (LAN) protocol processing in computers, network devices, and other data communications devices may be more efficient. A consistent inter-switch link frame format may be provided between a network interface peripheral device and other computer system components with which the device functions. Other advantages will become clear from the drawings, description and the claims that follow.